Electronic watermark system

ABSTRACT

An electronic watermark system invisibly embeds watermark information into original image data and the watermarked image data is transferred to a first medium. At the same time. the embedded watermark information is transferred to a second mediums. When a medium questioned is found, its watermark information can be easily identified by searching the second medium. Alternatively, the watermarked image data and the embedded watermark information are transferred to different storage areas of the same medium, respectively.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to an authorization system. andin particular to an authorization system using identificationinformation embedded into image data to prevent unauthorized duplicationof the image data.

2. Description of the Related Art

Recently, unauthorized copying of digital image data has become aserious problem because duplication of digital data can be extremelyeasy. To prevent unauthorized copying, several authorization systemusing identification information (an electronic watermark) embedded intoimage data have been proposed.

A visible-watermarking system is disclosed in Japanese Patent UnexaminedPublication No. 8-241403 which corresponds to U.S. Pat. No. 5,530,759.In this system, a visible, watermark is placed on a digital image suchthat the corresponding pixel of original image changes its brightnessbut its chromaticities.

An invisible-watermarking system is disclosed in NIKKEI ELECTRONICS1996.4.22 (no. 660). In this system, original image data is convertedinto frequency spectrum and then ID information is embedded into thefrequency spectrum which is in turn converted into image data invisiblyincluding the ID information. In authorization check, image dataquestioned is converted into frequency spectrum. ID information embeddedIn the image data questioned is obtained from a difference between thefrequency spectrum questioned and the original frequency spectrum. Sincethe ID information is embedded into frequency spectrum of the originalimage data, it has little effect on the image quality and further it hasbecome very difficult to delete the ID information from the image data.

In the above invisible-watermarking system, since the ID informationcannot be seen, it is difficult to check whether image data isauthorized in the case where no one knows the ID information.Especially, in a distribution system of data storing medium includingCD-ROMs, there are cases where a different watermark is used for eachdistribution channel. In this case, the authorization check andmanufacture management become very complicated and time-consuming jobs.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a system which canrapidly check whether image data is authorized to effectively preventunauthorized copying of the image data.

Another object of the present invention is to provide a system which caneasily identify an electronic watermark invisibly embedded in image datato check whether the image data is authorized.

According to an aspect of the present invention, watermarked image datahaving watermark information invisibly embedded is transferred to afirst medium and the embedded watermark information is transferred to asecond medium. Since the embedded watermark information is stored in thesecond medium, watermark identification can be easily made.

Further, in an authorization check system for checking whether a mediumquestioned is authorized, a storage stores watermark information andmedium identification information identifying a medium, the mediumsstoring watermarked image data which is produced by invisibly embeddingthe watermark information into original image data. A retrievalcontroller retrieves watermark information corresponding to mediumidentification information of the medium questioned from the storage. Awatermark extractor extracts watermark information questioned from imagedata stored in the medium questioned. A checker checks whether themedium questioned is authorized by comparing the extracted watermarkinformation with the retrieved watermark information.

According to another aspect of the present invention, watermarked imagedata having watermark information invisibly embedded and the embeddedwatermark information are both transferred to a single medium.Preferably, the embedded watermark information may be stored in adedicated storage area of the single medium. Further, the embeddedwatermark information may be encrypted and stored. Since the embeddedwatermark information is stored in the same medium, watermarkidentification can be easily made.

Further, in an authorization check system for checking whether a mediumquestioned is authorized, the medium questioned having a first storagearea for storing watermarked image data and a second storage area forstoring watermark information. After extracting watermark informationfrom image data stored in the medium questioned, a checker checkswhether the medium question is authorized by comparing the extractedwatermark information with the watermark information stored in thesecond storage area of the medium questioned.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 in a schematic block diagram showing an encoding sit of anelectronic watermark systems according to the present invention;

FIG. 2 is a schematic block diagram showing a watermark check section ofthe electronic watermark system according to the present invention;

FIG. 3 is a schematic diagram showing an example of watermarking sectionof the encoding side of FIG. 1;

FIG. 4 is a schematic diagram showing an example of a watermarkextractor of the watermark check section of FIG. 2;

FIG. 5 is a diagram showing a first embodiment of an electronicwatermark system according to the present invention;

FIG. 6 is a diagram showing an electronic watermark system according toa second embodiment of the present invention;

FIG. 7A is a schematic diagram showing an encoding side of an electronicwatermark system according to a third embodiment of the presentinvention; and

FIG. 7B is a schematic diagram showing a decoding side of the electronicwatermark system according to the third embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS ENCODING SIDE

Referring to FIG. 1, an encoding side of an electronic watermark systeminputs a stream of original image data D₀, and produces both MPEG(Motion Picture Experts Group) data stream D₄ and watermark data whichis invisibly embedded into the MPEG data D₄. More specifically, a streaminput section 101 inputs a stream of the original image data which isconverted to frequency spectrum data D₁ by a DCT (Discrete CosineTransform) section 102. A watermarking section 103 reads a watermarkD_(WM) selected from a plurality of watermarks stored in a watermarkdata table 104, and then embeds the selected watermark D_(WM) into thefrequency spectrum data D₁ to produce watermark-embedded frequencyspectrum data D₂. The watermark-embedded frequency spectrum data D₂ isquantized by a quantizing section 105 and the quantized data D₃ isencoded to produce MPEG data by an encoding section 106. A transfercontroller 107 inputs the MPEG data from the encoding section 106 toproduce a stream of the MPEG data D₄ and a transfer controller 108inputs the selected watermark D_(WM) from the watermark data table 104to produce selected watermark data. The stream of the MPEG data D₄ istransferred to a storage medium or a client through a commutationchannel and the selected watermark data is transferred to anotherstorage medium or the same storage medium, as will be described later(i.e., see FIGS. 5, 6 and 7A). Alternately, a transfer controller maytransfer the watermark image to a first medium and the watermarkinformation to as second medium utilizing a transfer controller as shownby the dotted line 107 a in FIG. 1.

It should be noted that the above sections 101-106 may be implementedwith a program-controlled processor such as CPU or DSP. In other words,the processor runs programs including the functions of the above section101-106 to perform the watermarking and MPEG data compression asdescribed above.

WATERMARK CHECKING SECTION

Referring to FIG. 2, in a watermark checking section of the electronicwatermark system, a stream data input section 201 inputs a stream ofMPEG data D₄′ and a watermark input section 202 inputs watermark dataassociated with the input MPEG data D₄′. The input MPEG data D₄′ isdecoded to produce data D₃′ by a decoding section 203 and then the dataD₃′ is inverse-quantized to produce data D₂′ by an inverse-quantizingsection 204. On the other hand, the watermark checking section isprovided with an original image memory 205 storing the original imagedata D₀. The original image data D₀ is converted to frequency spectrumdata D₁ by a DCT section 206.

When receiving the input frequency spectrum data D₂′ from the DCTsection 204 and the original frequency spectrum data D₁ from the DCTsection 206, a watermark extractor 207 extracts a watermark D_(WM1) fromthe input frequency spectrum data D₂′ by calculating a differencebetween the input frequency spectrum data D₂′ and the original frequencyspectrum data D₁. An inner product calculating section 208 inputs theextracted watermark D_(WM1) from the watermark extractor 207 and thereceived watermark D_(WM2) from the watermark input section 202, andperforms the inner product thereof to produce a degree of statisticalsimilarity between them. An authorization check section 209 checkswhether the extracted watermark D_(WM1) is Identical to the receivedwatermark D_(WM2) by comparing the degree of statistical similarity witha reference value.

The input MPEG data D₄′ may be received from a storage medium or acommunication network. The water k data associated with the input MPEGdata D₄′ is received from a management database storing manufacturemanagement data or the same storage medium as the MPEG data D₄′, as willbe described later. In the case where the input MPEG data D₄′ and/or thewater k data are received from a communication network, the watermarkchecking section is provided with a communication ms such as a networkinterface or a radio transceiver.

It should be noted that the above sections 201-209 may be implementedwith a program-controlled processor such as CPU or DSP. In other words,the processor runs programs including the functions of the above section201-209 to perform the watermark extracting, MPEG data decompression andauthorization check as described above.

WATERMARKING

Referring to FIG. 3, the watermarking section 103 receives the frequencyspectrum data D₁ from DCT section 102 and selects a set of N datesamples: f(1)-f(n) which are greater than a predetermined thresholdlevel from the frequency spectrum data D₁. Further, the watermarkingsection 103 selects a get of watermark data: w(1)-w(n) from randomnumbers depending on a normal distribution with a mean of 0 and avariance of 1. The watermarking section 103 calculates F(i)f(i)+α|f(i)|*(i) for each variable i (1≦i ≦n) using multipliers 301 and302, a constant α and an adder 303, where α it a scaling element(hereinafter, assuming α=1). The calculated data samples F(1)-F(n) aresubstituted for the selected N data samples f(1)-f(n) of the frequencyspectrum data D₁ to produce watermarked DCT frequency spectrum datawhich will be subject to inverse DCT In the following stage 105. In thismanner, the selected watermark D_(WM) is invisibly embedded into theoriginal image data D₀.

WATERMARK CHECK

Referring to FIG. 4, the watermark extractor 207 inputs the receiveddata samples F(1)-F(n) of the received frequency spectrum data D₂′ andthe original data samples f(1)-f(n) of the original frequency spectrumdata D₁. The watermark extractor 207 calculates w₁ (i)-(F(i)−f(i))/f(i)for each variable i (1≦i≦n) using subtracter 401 and a divider 402 toextract the watermark D_(WM1)=(W₁(1), W₁(2), . . . W₁(n)).

Subsequently, the inner product calculating section 208 calculates adegree of statistical similarity C between the extracted watermarkD_(WM1)=(W₁(1), W₁(2), . . . W₁(n)) and the received watermarkD_(WM2)=(W₂(1), W₂(2), . . . , W₂(n)) using the following equation:C=D_(WM1)* D_(WM2)/|D_(WM1)|*|D_(WM2)|. If C is equal to or greater thanthe predetermined level, it is determined that the received watermark isembedded into the received MPEG data D₄′ and therefore the received MPEGdata D₄ ′ is the authorized data. If C is smaller than the predeterminedlevel, it is determined that the received MPEG data D₄′ is anunauthorized duplication.

FIRST EMBODIMENT

Referring to FIG. 5, the encoding side of the electronic watermarksystem is comprised of a processor 501, the watermark data table 104, adata storage controller 502 and a data transfer controller 503. Asdescribed before. the processor 501 runs programs including thefunctions of the sections 101-106 as shown in FIG. 1 to perform thewatermarking and MPEG data compression.

The processor 501 inputs a stream of original image data D₀ and producesthe water-marked MPEG data stream D₄ which is stored onto a storagemedium 504 such as CD-ROM or magneto-optic disc by the data storagecontroller 502. At the same time, the data storage controller 502outputs a serial number of the storage medium 504 to the data transfercontroller 503. In this manner, an authorized medium 504 storing MPEGdata stream D₄ into which the selected watermark data D_(WM) is embeddedis manufactured. IF the processor 501 selects another watermark data, anauthorized medium 504 storing the same MPEG data stream D₄ into which adifferent watermark data is embedded is easily manufactured. Needless tosay, the data storage controller 502 outputs the serial, number of thestorage medium 504 to the data transfer controller 503.

The data transfer controller 503 inputs the embedded watermark dataD_(WM) from the watermark data table 104 and then transfers a pair ofthe embedded watermark data D_(WM) and the serial number of the storagemedium 504 to a manufacture management database 505 provided in amanagement center. Therefore, the watermark for each authorized medium504 can be easily identified by searching the manufacture managementdatabase 505, in the case where the management center is located at adistance from the encoding side, the data transfer controller 503 maytransfer them through a local-area network or a radio communicationchannel.

When a suspect medium 506 is found, the authorization check is performedby an authorization check section 507 running the programs Including thefunctions of the above sections 201-209 as shown in FIG. 2 to performthe watermark extracting, MPEG data decompression and authorizationcheck. In this case, the authorization check section 507 includes datacommunication means.

First of all, the authorization check section 507 reads the serialnumber from the suspect medium 506 and transmits a retrieval requestusing the read serial number to the manufacture management database 505through a network. Upon receipt of the retrieval request, themanufacture management database 505 is searched for the correspondingwatermark to the serial number. If the corresponding watermark is found,the retrieved watermark data is sent back to the authorization checksection 507.

Using the retrieved watermark data, the authorization check section 507perform the watermark extracting and watermark checking operations asdescribed before. That is, if the degree of statistical similarity Cbetween the extracted watermark and the retrieved watermark Is equal toor greater than the predetermined level, it is determined that themedium 506 is one of authorized media. If C is smaller than thepredetermined level, it is determined that the mediums 506 is anunauthorized duplication.

SECOND EMBODIMENT

Referring to FIG. 6, the encoding side of the electronic watermarksystem is comprised of a processor 601, the watermark data table 104, adata communication controller 602 and a data transfer controller 603. Asdescribed before, the processor 601 runs programs including thefunctions of the sections 101-106 as shown in FIG. 1 to perform thewatermarking and MPEG data compression.

The processor 601 inputs a stream of original image data D₀ and producesthe water-marked MPEG data stream D₄ which is transmitted to a client604 by the data communication controller 602. Here, it is assumed thatthe water-marked MPEG data is distributed depending on a datatransmission request received from the client 604. At the same time, thedata communication controller 602 outputs the address number of theclient 604 to the data transfer controller 603. In this manner, is MPEGdata stream D₄ into which the selected watermark data D_(WM) is embeddedis transmitted to the authorized client 604. If the data transmissionrequest is received from another client, the processor 601 selectsanother watermark data which is embedded into the MPEG data. The MPEGdata stream D₄ into which a different watermark data is embedded istransmitted to the new client. Needless to say, the data storagecontroller 602 outputs the address number of that new client to the datatransfer controller 603.

The data transfer controller 603 inputs the embedded watermark dataD_(WM) from the watermark data table 104 and then transfers a pair ofthe embedded watermark data D_(WM) and the client address number to amanufacture management database 605 provided in a management center.Therefore, the watermark for each authorized client 604 can be easilyidentified by searching the manufacture management database 605. In thecase where the management center is located at a distance from theencoding side, the data transfer controller 603 may transfer themthrough a local-area network or a radio communication channel. Furtherthe management database 605 is provided with data communicationcontroller 606.

When a suspect data provider 607 is found, the authorization check isperformed by an authorization check section 608 running the programsincluding the functions of the above sections 201-209 as shown in FIG. 2to perform the watermark extracting, MPEG data decompression andauthorization check. In this case, the authorization check section 508includes data communication means.

First of all, the authorization check section 608 receives the addressnumber from the suspect data provider 607 and transmits a retrievalrequest using the address number to the manufacture management database605 through the data communication controller 606. Upon receipt of theretrieval request, the manufacture management database 605 is searchedfor the corresponding watermark to the address number. If thecorresponding watermark is found, the retrieved watermark data is sentback to the authorization check section 608.

Using the retrieved watermark data the authorization check section 608perform the watermark extracting and watermark checking operations asdescribed before. That is, if the degree of statistical similarity Cbetween the extracted watermark and the retrieved watermark is equal toor greater than the predetermined level, it is determined that the dataprovider 607 is one of authorized clients. If C is smaller than thepredetermined level, it is determined that the data provider 607distributes an unauthorized duplication.

THIRD EMBODIMENT

Referring to FIG. 7A. the encoding side of the electronic watermarksystem is comprised of a processor 701, the watermark data table 104, anencryption section 702 and a data storage controller 703. As describedbefore, the processor 701 runs program including the functions of thesections 101-106 as shown in FIG. 1 to perform the watermarking and MPEGdata compression. Further, the processor 701 may include the encryptionsection 702 and the data storage controller 703.

The processor 701 inputs a stream of original image data D₀ and producesthe water-marked MPEG data stream D₄ which is stored onto a storagemedium 704 such as CD-ROM or magneto-optic disc by the data storagecontroller 703. At the same time, the encryption section 702 encryptsthe selected watermark data D_(WM) and the encrypted watermark data isstored onto the same storage medium 704 by the data storage controller703. It is preferably that the storage medium 704 has a first area 705for storing the water-marked MPEG data and a second area 706 dedicatedto the encrypted watermark data. In the case of MPEG data reading mode,no data can read from the second area 706.

In this manner, an authorized medium 704 storing the encrypted watermarkdata D_(WM) and the watermarked MPEG data stream D₄ is manufactured. Ifthe processor 701 selects another watermark data, an authorized medium704 storing the new watermark data and the same MPEG data stream D₄ intowhich the new watermark data is embedded is easily manufactured.

Referring to FIG. 7B, when a suspect medium 707 is found, theauthorization check is performed by cm authorization check section 708running the programs including the functions of the above sections201-209 as shown in FIG. 2 to perform the watermark extracting, MPEGdata depression and authorization check. In this case, the authorizationcheck section 708 includes decryption section 709.

First of all, the decryption section 709 reads the watermark data fromthe second area dedicated to watermark of the suspect medium 707 anddecrypts it to output watermark data D_(WM)′ to the authorization checksection 708. Using the read watermark data D_(WM)′, the authorizationcheck section 708 performs the watermark extracting and watermarkchecking operations as described before. That is, if the degree ofstatistical similarity C between the extracted watermark and the readwatermark D_(WM)′ is equal to or greater than the predetermined level,it is determined that the medium 707 is one of authorized media. If C issmaller than the predetermined level, it is determined that the medium707 is an unauthorized duplication.

As described above, since the authorized watermark can be easilyobtained from a management center or the storage medium storing thewatermarked MPEG data, the authorization check is rapidly performed withreliability.

What is claim is:
 1. A system comprising: an information generator forgenerating watermark information; a combiner for invisibly embedding thewatermark information into original image data to produce watermarkedimage data; and at least one transfer controller for separatelytransferring the watermarked image data and the watermark informationreceived from the information generator to a first storage medium and asecond storage medium, respectively and watermark information notincluding a verification key for decoding the watermark image datawherein the first medium and second medium are physically in the samelocation; wherein said transfer controller encrypts the watermarkinformation for storage only in the second medium which is dedicated tothe encrypted watermark information so that only the encrypted watermarkinformation is allowed to be read.
 2. The system according to claim 1,wherein the at least one transfer controller further transfers mediumidentification information identifying the first storage medium to thesecond storage medium.
 3. The system according to claim 2, wherein thesecond storage medium stores the encrypted watermark information and themedium identification information to allow retrieval.
 4. The systemaccording to claim 3, wherein the medium identification information is amanufacture serial number of the first storage medium.
 5. A systemcomprising: an information generator for generating watermarkinformation: a combine for invisibly embedding the watermark informationinto original image data to produce watermarked image data; and atransfer controller for transferring both the watermarked image data andthe watermark information received from the information generator fromthe combine to a single medium, said watermark information not includinga verification key for decoding the watermarked image data; wherein thetransfer controller encrypts the watermark information and transfersencrypted watermark information to the single medium; and wherein in thesingle medium is a storage medium having a first storage area forstoring the watermarked image data and a second storage area for storingthe encrypted watermark information, wherein the second storage area isdedicated to the encrypted watermark information so that only theencrypted watermark information is allowed to be read.
 6. Anauthorization check system for checking whether a medium questioned isauthorized, the medium questioned having a first storage area forstoring watermarked image data and a second storage area for storingencrypted watermark information, the system comprising: a watermarkextractor for extracting said encrypted watermark information questionedfrom image data stored in the medium questioned using the original imagedata and not utilizing a verification key for extracting said encryptedwatermark information; and a checker for checking whether the mediumquestioned is authorized by comparing the extracted encrypted watermarkinformation with the encrypted watermark information stored in thesecond storage area of the medium questioned; wherein the second storagearea is dedicated to the encrypted watermark information so that onlythe encrypted watermark information is allowed to be read.
 7. A methodfor checking whether a medium questioned is authorized, comprising thesteps of: generating watermark information; generating encryptedwatermark information; invisibly embedding the watermark informationinto original image date to produce watermarked image data; transferringthe watermarked image data to a first storage area of an authorizedstorage medium and the encrypted watermark information a second storagearea of the authorized storage medium; extracting watermark informationstored in the medium questioned; and extracting watermark informationfrom watermarked image data stored in the medium question using theoriginal image data and not utilizing a verification key for extractingsaid watermark information; checking whether the medium questioned isauthorized by comparing the extracted watermark information withwatermark information stored in the medium questioned; and wherein thesecond storage area is dedicated to the encrypted watermark informationso that only the encrypted watermark information is allowed to be read.8. The method according to claim 7, wherein the authorized medium is astorage medium having a first storage area for storing the watermarkedimage data and a second storage area. for storing the watermarkinformation, wherein the second storage area to dedicated to thewatermark information so that only the watermark information is readabletherefrom.
 9. The method according to claim 8, wherein the watermarkinformation is encrypted and encrypted watermark information is storedto the authorized medium.
 10. The system according to claim 1, whereinthe information generator generates the watermark information from aplurality of watermark information candidates.
 11. The system accordingto claim 5, wherein the information generator generates the watermarkinformation from a plurality of watermark information candidates. 12.The method according to claim 7, wherein the step of generating thewatermark information includes the step of selecting the watermarkinformation from a plurality of watermark information candidates. 13.The method according to claim 7, wherein the watermarked image data andthe watermark information are transferred over a network.
 14. The methodaccording to claim 13, wherein the watermarked image data and thewatermark information are transferred over the same network.